The purpose of this investigation is to attempt to ascertain the nature of developmental regulatory systems whose modification during embryogenesis may result in altered neural tube development (e.g., anencephaly, exencephaly, or spina bifida). The studies focus on: (1) the problems associated with staging teratogenic responsiveness in offspring of the rat or mouse; (2) characterization of the behavior of those plasma membranal enzymes (e.g., prostaglandin synthetase, (Na ion plus K ion) ATPase, and adenyl cyclase) which are likely to play a significant role in determining responsiveness of embryonic cells to teratogenic stresses, namely, those due to deficiencies in essential nutrients, to drugs and to environmental agents.